Pairwise Testing | What It Is, When & How to Perform?

In this complete guide, we’ll break down the process of pairwise testing into simple steps that anyone can follow. We’ll cover everything from selecting input parameters to creating test cases and analyzing results. Whether you’re a beginner or an experienced software tester, this guide has something for everyone. So grab a cup of coffee and get ready to learn how to perform pairwise testing like a pro!

What is Pairwise Testing?

Pairwise testing, or you can also call it all-pairs testing, is a P&C(Permutations and combinations)based software testing technique that tests each pair of input parameters to verify that the system functions correctly for all possible discrete combinations.

It is based on covering all possible discrete combinations of input parameters by using a minimum set of test cases. This technique is helpful when the number of input parameters is large, as it helps to reduce test execution time and cost.

Let’s say you have an application that allows users to enter two numbers, and the application will output the sum of the two numbers. You can use pairwise testing to test all possible combinations of two numbers, such as (1, 2), (2, 3), (3, 4), (4, 5), etc. By testing all the combinations of two numbers, you can be sure that the application is working correctly and will not fail when given different numbers.

What is the Purpose of Pairwise Testing?

Pairwise testing aims to ensure that all possible discrete combinations of inputs have been tested without the need to test every single combination. This can reduce the time and effort required for testing and the number of test cases that need to be written.

Examples of Pairwise Testing

Here are some more simple examples of this type of testing:

1. For example, when testing the length of a line segment, pairwise testing would involve testing all combinations of line lengths, such as 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4. In this example, pairwise testing tests a line segment’s length. This means that all possible combinations of line lengths are being tested to ensure the accuracy of the length measurement. For example, the length of a line segment could be 1 unit, 2 units, 3 units, or 4 units, so all possible combinations of these lengths must be tested to ensure accuracy. This includes testing 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4. This allows for detecting any discrepancies or errors in the measurement of the line segment.

2. One more example is where Pairwise testing can also test relationships between two variables. When testing the relationship between the size of a circle and its circumference, pairwise testing would involve testing all combinations of circle sizes (radius) and corresponding circumference values, such as 1-3.14, 2-6.28, 3-9.42, etc.

In this example, the two variables being tested are a circle’s size (radius) and the circumference of that same circle. To test this relationship, pairwise testing would involve testing all combinations of circle sizes (radius) and corresponding circumference values.

The test would evaluate a circle with a radius of 1 and a circumference of 3.14, a circle with a radius of 2 and a circumference of 6.28, and a circle with a radius of 3 and a circumference of 9.42. By testing all possible combinations, the relationship between the size of a circle and its circumference can be determined.

3. Can Pairwise testing be used to test combinations of different probabilities? Yes, For example, when testing the probability of an event occurring, pairwise testing would involve testing all combinations of probabilities, such as 0.1-0.2, 0.2-0.3, 0.3-0.4, etc.

Explaining this example, the tester could examine how the probability of an event occurring changes when the probability of a second event occurring increases from 0.1 to 0.2, from 0.2 to 0.3, from 0.3 to 0.4, etc. This type of testing can be used to identify edge cases and potential problems in the system.

Objectives of Pairwise Testing

Pairwise testing aims to ensure that all possible discrete combinations of inputs have been tested without the need to test every single combination. This can reduce the time and effort required for testing and the number of test cases that need to be written. The main advantage of Pairwise testing is that it enables the tester to identify errors that may occur when two or more different parameters are combined. This is important as errors may occur in combinations of parameters that are not tested individually.

For example, a program may work correctly when you input two numbers but may cause an error when you input two different numbers. By testing all possible combinations of parameters, the tester can identify these types of errors. Pairwise testing is especially useful when testing complex software with many parameters. By testing all possible combinations of parameters, the tester can ensure that no errors occur in any combination. This helps ensure that the software works correctly in all scenarios, which is essential for producing reliable and bug-free software.

When to Use Pairwise Testing?

Pairwise testing is helpful when testing complex systems that have multiple input parameters and multiple possible values for each parameter. It can significantly reduce the number of test cases that need to be created while ensuring that all possible discrete combinations of parameters are tested. This can help reduce test case creation time and cost and improve the software’s overall quality. Pairwise testing is not appropriate for all types of software testing. As we discussed, it is most effective for systems with multiple parameters and multiple possible values for each parameter. If a system has only a few parameters and a small number of possible values for each parameter, pairwise testing may be unnecessary. Pairwise testing, also, will not be useful if the values of inputs are inappropriate.

Further, pairwise testing may not be the most effective technique in cases where the order of parameters is important, as this type of testing does not account for ordering.

Should Pairs Testing be Automated?

Pairwise testing is a technique where you test all possible combinations of input parameters in pairs to find defects that might not appear in normal testing. It’s a great way to save time and increase test coverage, but it can be tedious and time-consuming if done manually. That’s where automation comes in. By automating pairwise testing, you can save time and effort while ensuring thorough coverage. For example, you’re testing a web application with multiple input fields like name, email, phone number, etc.. Using an automated pairwise testing tool. You can quickly generate test cases that cover all possible combinations of these inputs without manually creating each one.

Of course, there are some downsides to consider as well. Automated pairwise testing requires a certain level of expertise and can be more complex to set up than manual testing. Luckily, some tools are available to generate these test cases, like: Hexawise, All Pairs, Testcover, pairwise, Allpairs.

Once you have the generated test cases, you can also automate them via some black box testing tool like Testsigma. With Testsigma, a no-code test automation tool, you can automate your front-end tests for web, mobile, and desktop from the same place 5x faster. The test case creation and maintenance is as easy as writing sentences in simple English. Testsigma is also available as an opensource and free-forever version.

How to Automate All-Pairs Testing with Testsigma?

Watch the video and see how to perform All-Pairs testing using Testsigma:

What are the Benefits of Pairwise Testing?

The benefits of all pairs testing are many. One of the main benefits of pairwise testing is that it can help identify defects that may not be discovered through other testing methods. For example, consider a software application that allows users to customize the font and color of their text. Testing all possible combinations of these variables without all pairs testing would be difficult. However, by pairwise testing, testers can quickly and efficiently generate test cases that cover all possible combinations of font and color. This can help ensure that the software functions as expected and that users are not experiencing unexpected issues or errors. This can reduce the number of tests you need to run by 50% or more.

Disadvantages of Pairwise Testing

Pairwise testing can be tedious and time-consuming. One of the problems of pairwise testing could be that you have to complete a huge number of test cases to ensure all the combinations of inputs are covered. 

Pairwise testing relies on all pairs of parameters interacting to determine the results, and sometimes, this assumption may be false. Incorrect assumptions like this can prevent bugs from being caught in testing.

Also, additional tests must sometimes be added to supplement the pairwise tests. This adds additional testing time and effort. 

Challenges in Pairwise Testing

There are some challenges that one may face when implementing pairwise testing.

• One of the major challenges is identifying the right set of input parameters.
• It’s important to select relevant and meaningful input parameters that would affect the behavior of the software.
• If you don’t select carefully, your test coverage may not be thorough enough, and you may miss some defects.
• Challenging to accurately determine the interactions between parameters, which may lead to selecting the wrong combinations.

But don’t worry; You can overcome this challenge with some experience, trial, and error.

Using Pairwise Testing To Speed Up Cross-Browser Testing

To use pairwise testing for cross-browser testing, you must first identify the parameters you want to test. For example, you might want to test the following parameters:

• Browser
• Operating system
• Device type
• Screen resolution

Once you have identified the parameters you want to test, you can use a pairwise tool to generate test cases.

Here is an example of a real-world scenario where you could use pairwise testing for cross-browser testing:

You are developing a new e-commerce website. You want to test the website on various browsers and operating systems to ensure it is compatible with all major platforms.

You could use pairwise testing to generate a set of test cases that covers all possible combinations of two parameters. For example, you could generate a set of test cases covering all possible combinations of browsers and operating systems.

Here is an example of a pairwise test case for cross-browser testing:

• Browser: Chrome
• Operating system: Windows 10

You would then execute this test case on a machine that is running Chrome on Windows 10. You would repeat this process for all of the other pairwise test cases.

Tools list for Pairwise Testing

Pairwise testing tools automate the test case design process by generating a compact set of parameter value choices as the desired test cases. This is done by applying the all-pairs testing technique, which involves testing all possible combinations of two parameters.

Some well-known pairwise testing tools from the industry include:

• PICT – Pairwise Independent Combinatorial Testing (Microsoft)
• IBM FoCuS – Functional Coverage Unified Solution (IBM)
• ACTS – Advanced Combinatorial Testing System (NIST)
• Hexawise
• Jenny
• Pairwise (Inductive AS)
• VPTAG free All-Pair Testing Tool

Pairwise testing tools are especially useful for testing systems with many parameters, as they can significantly reduce the number of test cases that need to be executed.

Summary

The idea behind pairwise testing is to test every possible pair of inputs. Pairwise testing reduces the number of test cases required to cover all possible combinations of input parameters, making the testing process more efficient and effective. This technique is particularly useful when many input parameters need to be tested, as it helps reduce the time and resources required for testing.

Frequently Asked Questions

Is pairwise testing completely automatic?

No, pairwise testing is not entirely automatic. This type of testing is usually performed manually and requires an organized approach to systematically explore all possible combinations of input parameters and document any bugs or issues encountered.

How effective is pairwise testing at finding bugs?

Pairwise testing can be highly effective at finding bugs in a system. It is especially effective in finding bugs associated with interactions between different system parts, which can be challenging to uncover using traditional testing methods. 

Here is a simple example of how pairwise testing can find bugs:

Imagine a system with three parameters:

• Parameter 1: Can be either “Enabled” or “Disabled”
• Parameter 2: Can be either “True” or “False”
• Parameter 3: Can be either “1” or “2”

If we test all possible combinations of these parameters, we must execute 8 test cases (2^3). However, pairwise testing can reduce the number of test cases to 3.

Here are the 3 pairwise test cases:

• Parameter 1: Enabled, Parameter 2: True, Parameter 3: 1
• Parameter 1: Disabled, Parameter 2: False, Parameter 3: 2
• Parameter 1: Enabled, Parameter 2: False, Parameter 3: 1

These 3 test cases cover all possible combinations of two parameters.

If there is a bug in the system, it is likely to be exposed by one of these 3 test cases.